Stripline, microstrip and other transmission line type filters have been used in electronic devices to provide inexpensive filters which are of small size. In such filters, the frequency response depends upon the configuration of the conducting resonator and the shape and dielectric constant of the surrounding materials. In small devices for use at very high frequencies, such as 800 MHz, the length of the resonator is quite critical, and variations in the length of the resonator and the dimensions of the dielectric substrate on which it is placed resulting manufacturing tolerances can result in changes in the frequency response so that the response of the completed filter will not fall within acceptable limits. In particular, stripline filters constructed by known thin film processes may have variations in the resonator configuration resulting from errors in alignment of the mask used in forming the resonator, which result in unsatisfactory frequency responses.
The use of external devices for adjusting the frequency response of filters is known, such as trimming screws and capacitors, but these devices substantially increase the size and cost of the filters. It has also been proposed to adjust components of the filter after it is constructed and tested, but this requires further processing steps. These various adjusting devices and techniques have not been entirely satisfactory in many applications.